1. Technical Field of the Invention
This invention relates to devices for preventing the bubbles and froth that collects as gas out of an extracorporeal blood handling system; and more particularly to a gas trap for separating the bubbles from the blood and periodically expelling the gas from the blood handling system when a self actuating ball stopper valve indicates accumulated gas volume is excessive.
2. Background Art
Extracorporeal blood treatment involves removing blood from a patient, treating the blood external to the patient and returning the treated blood to the patient. Occasionally, bubbles form in the blood during extracorporeal blood treatment as a result of leakage of air into the blood at the point blood is withdrawn from the patient for extracorporeal treatment or as a result of leakage of air at points of connection in the extracorporeal treatment system. Bubbles also form as a result of turbulence of the blood flowing in the extracorporeal treatment system and coalescence of gases in the blood during treatment, among other causes. Care must be taken to remove bubbles from the blood prior to returning the blood to the patient and, to the extent possible, prevent formation of bubbles in the blood during treatment. Blood returned to the patient which contains bubbles creates a risk of serious health consequences to the patient.
Most extracorporeal treatment systems incorporate chambers for removal of bubbles from blood treatment. These chambers, often referred to as bubble traps, provide an opportunity for bubbles in the blood to separate from the blood while the blood is in the chamber. Bubbles in the blood rise to the surface of the blood in the chamber. Bubbles in the blood may also separate from the blood as the blood is delivered to the chamber, when the blood is delivered dropwise or in a stream over the surface of the blood already present in the chamber. The gas from the bubbles which collects above the level of blood is mechanically removed from the chamber, or is allowed to remain in the chamber until extracorporeal treatment is complete.
Conditions under which bubbles form in the blood during extracorporeal treatment may be exacerbated by higher blood flow rates. For example, blood entering a bubble trap apparatus at a high rate can froth and create bubbles in the blood present in the bubble trap apparatus. Various geometries have been explored to minimize this contribution to the problem.
When blood is introduced into a bubble trap apparatus below the upper surface of the blood already present in the apparatus, stagnation and clotting have a tendency to occur in the blood near the upper surface of the blood. Stagnation and clotting occur near the upper surface of blood because the newly introduced blood tends to flow downward and often does not mix with blood above the point of introduction and near the upper surface. Some prior art indicates that incoming fluid should be admitted at the top of the chamber so as not to be submerged under fluid already in the chamber. Tangential inlets are known to reduce the turbulence of the inlet stream impacting the fluid in the chamber.
Within the human body, blood is circulated under heart pumping pressures of about 100-200 mm Hg, millimeters of Mercury, or about two to four pounds per square inch. Extracorporeal blood handling systems may exceed these pressures somewhat to achieve the desired flow rates through filters, lines and blood treating components.
Cleanliness is of paramount concern in medical applications involving the recycling of bodily fluids back into the body. Ease of maintenance of the reusable components of blood handling devices is important.
Examples of current art that may provide the reader with useful context for bubble traps are Brugger""s U.S. Pat. No. 5,591,251, published Jan. 7, 1997 and Brugger""s U.S. Pat. No. 5,674,199, published Oct. 7, 1997; Schnell""s U.S. Pat. No. 6,019,824, published Feb. 1, 2000, Schnell et al""s U.S. Pat. No. 6,071,269, published Jun. 6, 2000; and Schnell et al""s U.S. Pat. No. 6,117,342, published Sep. 12, 2000.
There are similar problems with excessive gas bubbles in pressurized liquids in other arts. Various designs of foam traps are presently in commercial use in the carbonated beverage and beer industry to prevent the entrance of excessive foam into the distribution lines as the keg hits empty, with shutoff valves that hold the liquid in the lines while the empty keg is being replaced or the system is being switched to an already connected next keg. The prior art of Francisco Moreno Barbosa, UK Patent GB2286581, is instructive, as are the examples of commercial products accompanying this application. Most devices use a float to seal the outlet of a reservoir to which the beer lines are attached when the level of liquid in the reservoir falls low. There is an alternate device that operates on a fluid momentum theory; gas versus liquid.
There are many commercial and industrial processes that use gas-propelled liquid pumping or dispensing systems, where it is likewise desirable to prevent or control the amount of foam entering the distribution lines. Liquid dispensing systems using vented containers and mechanical pumps are also subject to the same problem, when the liquid level in a vented tank or container falls to level of the outflow port or suction tube so that air is being sucked into the pump along with the residual liquid. It is to the extracorporeal circulating of blood, as well as other applications in which bubbles and/or foam present in the fluid is a problem, to which the instant invention is addressed.
It is among the objects of the invention to keep the distribution lines that transport the blood or other liquid in a mechanically pumped or gas propelled liquid dispensing system, full of liquid at all times, and free of propellant gas, air, or foam, by utilizing a novel bubble trap connectable to a liquid container or a manifold to which are connected multiple containers.
It is further among the objects of the invention to employ the trap in an automated control system on a liquid dispensing system pre-connected by a manifold to multiple containers, to sequence the containers when empty without introducing gas or air into the dispensing system.
The foam trap has a reservoir or chamber into which the liquid is piped. The chamber is of suitable interior volume with respect to the viscosity and flow rate of the liquid to act as a coarse gravity separator of the liquid and gas when gas enters the supply line from the container. The chamber has two outlets, an upper gas vent outlet for discharge, and a lower liquid outlet to which the distribution lines are attached. Each outlet is configured with a horizontally oriented valve seat suitable to accept a vertically displaced spherical closing member or floating ball stopper in a sealing relationship. Within the chamber there is a free floating ball stopper for each valve seat, suitable for sealing its respective valve seat when moved and held against it by pressure or gravity. The foam trap also has externally accessible mechanisms for restraining the seating of or for unseating either of the balls independently, when desired. The geometry of the chamber, valves and balls is such that the balls do not compete for either valve seat when both are afloat in rising or falling liquid.
To initiate use, the liquid outlet ball sealing restraint is put in place to insure that the outlet port ball stopper is loose, and the gas vent outlet hall seating restraint is disengaged or removed to allow automatic closure. When liquid enters the chamber from the liquid containers, both ball stoppers are raised with the rising liquid level, and the gas vent ball is floated into place on the vent valve seat, closing the vent port. The ball stopper is held in place by the pressure of the liquid and gas in the system. When maximum pressure is reached, the liquid outlet ball sealing restraint is removed to permit automatic closure, but the liquid outlet ball stopper is still being floated by the liquid in the chamber so the liquid outlet remains open to pass liquid through the lines to the dispensing point until the liquid level drops.
When the container in use is exhausted and xe2x80x9ckicksxe2x80x9d, and the liquid in the trap chamber goes low as it is replaced by propellant gas or air in the system, the liquid outlet is closed and sealed by its ball stopper so that gas or air does not enter the distribution lines. Meanwhile, the gas vent ball stopper remains in place under pressure, maintained by a check valve at the container end of the liquid supply line. Sensing the low pressure in the dispensing line, the operator or the system controller changes or switches to a full container and the supply of liquid is re-established. Thereupon, the gas vent ball stopper is the unseated to open the vent port, and the restraint then removed. This permits the flow of liquid into the chamber to empty the gas and reseat the vent ball. When the vent has closed and the chamber has stabilized at maximum pressure, the liquid outlet ball stopper is unseated and the restraint then removed to resume normal operation.
It is further among the objects of the invention to provide a foam trap that is constructed of materials suitable for contact with blood, rugged and reliable, simple to use, hygienic in that it has minimal internal crevices is easy to disassemble, clean and maintain, and is suitable for regulatory approval. It is yet further among the objects of the invention to utilize principles of symmetry of design and commonality of parts for similar functions to minimize the number of unique parts.
It will be apparent to those skilled in the art, that the invention functions with carbonated or gaseous liquids or fluids, with mixtures of gas and liquid, and with liquids or fluids that are either gas-propelled or mechanically pumped from a container into which replacement air or gas or gaseous fluid flows.
Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein we have shown and described only a preferred embodiment of the invention, simply by way of illustration of the best mode contemplated by us in carrying out our invention.